/* ===== Reset & Base ===== */
*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }

body {
  font-family: 'Segoe UI', system-ui, -apple-system, sans-serif;
  background: #f0f4f8;
  color: #333;
  min-height: 100vh;
}

/* ===== Landing Page ===== */
.site-header {
  background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
  color: white;
  text-align: center;
  padding: 2.5rem 1rem 2rem;
}
.site-header h1 { font-size: 2.2rem; font-weight: 800; }
.site-header .subtitle { margin-top: .4rem; opacity: .85; font-size: 1.05rem; }

.container { max-width: 1100px; margin: 0 auto; padding: 2rem 1rem; }

.grades-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(300px, 1fr));
  gap: 1.5rem;
}

.grade-card {
  background: white;
  border-radius: 16px;
  overflow: hidden;
  box-shadow: 0 2px 12px rgba(0,0,0,.08);
  transition: transform .2s, box-shadow .2s;
}
.grade-card:hover { transform: translateY(-4px); box-shadow: 0 8px 24px rgba(0,0,0,.12); }

h2.grade-card-header,
.grade-card-header {
  padding: 1.2rem 1.5rem;
  color: white;
  font-size: 1.3rem;
  font-weight: 700;
  display: flex;
  align-items: center;
  gap: .6rem;
  margin: 0;
}
.grade-card-header .icon { font-size: 1.6rem; }

.grade-card-body { padding: 1rem 1.5rem 1.5rem; }

.book-item {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: .7rem 0;
  border-bottom: 1px solid #eee;
}
.book-item:last-child { border-bottom: none; }

.book-item-title { font-weight: 500; }

.btn {
  display: inline-flex;
  align-items: center;
  gap: .35rem;
  padding: .45rem 1rem;
  border: none;
  border-radius: 8px;
  font-size: .85rem;
  font-weight: 600;
  cursor: pointer;
  text-decoration: none;
  transition: background .15s;
}
.btn-view { background: #667eea; color: white; }
.btn-view:hover { background: #5a6fd6; }
.btn-download { background: #e8ecf1; color: #444; }
.btn-download:hover { background: #dde1e8; }

.book-actions { display: flex; gap: .5rem; }

.empty-grade {
  color: #999;
  font-style: italic;
  padding: .5rem 0;
  font-size: .95rem;
}

footer {
  text-align: center;
  padding: 2rem 1rem;
  color: #888;
  font-size: .9rem;
}

/* ===== Viewer Page ===== */
.viewer-header {
  background: #2d3436;
  color: white;
  padding: .75rem 1.2rem;
  display: flex;
  align-items: center;
  justify-content: space-between;
  flex-wrap: wrap;
  gap: .5rem;
}
.viewer-header .back-link {
  color: white;
  text-decoration: none;
  font-weight: 600;
  font-size: .95rem;
  display: flex;
  align-items: center;
  gap: .3rem;
}
h1.book-title,
.viewer-header .book-title { font-weight: 700; font-size: 1.1rem; margin: 0; }
.viewer-header .page-info { font-size: .9rem; opacity: .8; }

.viewer-body {
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  min-height: calc(100vh - 120px);
  background: #1a1a2e;
  padding: 1rem;
  position: relative;
}

#flipbook-container {
  position: relative;
  /* sized dynamically by JS */
}

.viewer-controls {
  background: #2d3436;
  padding: .6rem 1rem;
  display: flex;
  align-items: center;
  justify-content: center;
  gap: .75rem;
  flex-wrap: wrap;
}

.ctrl-btn {
  padding: .5rem 1.1rem;
  border: none;
  border-radius: 8px;
  font-size: .85rem;
  font-weight: 600;
  cursor: pointer;
  transition: background .15s;
}
.ctrl-prev, .ctrl-next { background: #667eea; color: white; }
.ctrl-prev:hover, .ctrl-next:hover { background: #5a6fd6; }
.ctrl-print { background: #00b894; color: white; }
.ctrl-print:hover { background: #00a381; }
.ctrl-download { background: #fdcb6e; color: #333; }
.ctrl-download:hover { background: #f9bf3b; }

.ctrl-btn:disabled { opacity: .4; cursor: not-allowed; }

/* Loading overlay */
.loading-overlay {
  position: fixed;
  inset: 0;
  background: rgba(26,26,46,.92);
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  z-index: 100;
  color: white;
}
.spinner {
  width: 48px; height: 48px;
  border: 5px solid rgba(255,255,255,.2);
  border-top-color: #667eea;
  border-radius: 50%;
  animation: spin .8s linear infinite;
}
@keyframes spin { to { transform: rotate(360deg); } }
.loading-overlay p { margin-top: 1rem; font-size: 1.1rem; }
.loading-overlay .progress-text { margin-top: .3rem; opacity: .7; font-size: .9rem; }

.hidden { display: none !important; }

/* Page styling inside flipbook */
.page-canvas {
  background: white;
}

/* Responsive */
@media (max-width: 600px) {
  .site-header h1 { font-size: 1.5rem; }
  .grades-grid { grid-template-columns: 1fr; }
  .viewer-header { font-size: .85rem; }
  .ctrl-btn { padding: .4rem .8rem; font-size: .8rem; }
}